The invention relates generally to compression refrigeration systems and, more particularly, to compression refrigeration systems having improved motor cooling.
In a compression system, a motor is provided for driving a compressor mechanism. The size and type of the motor required depends upon several factors, including the capacity of the compressor and the operating environment of the compression system. Providing adequate motor cooling without sacrificing energy efficiency of the compression system remains challenging, especially in large-capacity systems. Centrifugal compressors are often used in refrigeration systems. Centrifugal compressors are usually driven by electric motors that are commonly included in a housing that encases both the motor and the compressor. The motor must therefore be cooled using a cooling medium, such as the refrigerant from the main refrigerant cycle for example.
In known motor cooling methods, liquid refrigerant is sourced from the high-pressure line between the condenser and the expansion device. The refrigerant is injected into the motor housing where it absorbs motor heat and rapidly evaporates or flashes into gaseous form, thus cooling the motor. Conventional motor assemblies include an overhung motor arrangement, where an unsupported end of the rotor is easily accessible within the housing. In such systems, the liquid refrigerant is sprayed into the unsupported end of the motor. The refrigerant travels through axial and radial holes cooling the rotor until reaching the air gap between the rotor and the stator. New compressor motor assemblies, however, may include a rotor shaft that is simply supported at both ends. Because the rotor is no longer easily accessible at one end, the liquid refrigerant cannot be sprayed into the core of the rotor.